1. Field of the Invention
The present invention relates to a hydrogen permeable membrane which has an excellent high-temperature amorphous stability, i.e., the quality of stably maintaining non-crystallinity for a long period of time when held in a high-temperature state, and which when used as a hydrogen permeable membrane in an apparatus such as a high-performance hydrogen purifier thus makes it possible to carry out a high-temperature heating operation that enhances the productivity of such a high-performance hydrogen purifier.
2. Description of the Related Art
“Green energy” has attracted much attention in recent years as a way to counteract such phenomena as atmospheric pollution and global warming. In particular, energy systems which use hydrogen gas (one type of green energy) as the fuel, such as hydrogen fuel cells and hydrogen gas turbines, are currently under active investigation.
The high-purity hydrogen gas used as the fuel gas in these energy systems is produced from a hydrogen-containing feed gas such as a mixed gas obtained by electrolyzing water or a mixed gas obtained by steam reforming liquefied natural gas (LNG). Such production is typically carried out using a high-performance hydrogen purifier like that shown schematically in FIG. 1 which is divided into a left-hand chamber and a right-hand chamber by a hydrogen permeable membrane that is made of a material permeable only to hydrogen and is reinforced at the periphery with a frame made of nickel or the like. A hydrogen-containing feed gas inlet and a bleed gas outlet are attached to the left-hand chamber, a high-purity hydrogen gas outlet is attached to the right-hand chamber, and a reaction chamber made of a material such as stainless steel is provided at the center. The feed gas is passed through the hydrogen permeable membrane with the reaction chamber heated to 200 to 300° C., thereby producing high-purity hydrogen gas by separative purification.
Hydrogen permeable membranes of this type which are made of non-crystalline nickel-zirconium or zirconium-nickel alloys are known. Processes for fabricating such membranes are known to include a liquid quenching process in which an alloy melt of a given composition is sprayed onto the surface of, for example, a rapidly rotating copper roll to effect solidification to a film thickness of 5 to 500 μm (e.g., see JP-A 2000-256002).
To enhance productivity, there is a trend among such high-performance hydrogen purifiers toward operation under high-temperature heating. In prior-art high-performance hydrogen purifiers which use hydrogen permeable membranes made of non-crystalline nickel-zirconium alloys, during operation at a high heating temperature above 300° C., the hydrogen permeable membrane which exhibits a high hydrogen-separating and permeating ability owing to its non-crystallinity is readily subject to localized crystallization. In the areas that have crystallized, the hydrogen permeating and purifying ability of the membrane markedly declines, as a result of which the passage through the membrane and admixture of impurity gases other than hydrogen cannot be avoided. Accordingly, such hydrogen permeable membranes have a relatively short service life.
There also exists a strong need for an even higher performance and a smaller size than has hitherto been achieved in high-performance hydrogen purifiers. This need has created in turn a strong desire for hydrogen permeable membranes endowed with a greater hydrogen-separating and permeating ability.